Path: news.eternal-september.org!eternal-september.org!feeder3.eternal-september.org!nntp-feed.chiark.greenend.org.uk!ewrotcd!.POSTED.chiark.greenend.org.uk!not-for-mail From: Theo Newsgroups: sci.electronics.design Subject: Re: Mid-span ethernet monitor Date: 08 Jun 2025 14:52:27 +0100 (BST) Organization: University of Cambridge, England Message-ID: References: <1020c8h$2oq18$1@dont-email.me> <1021obu$1rm1$1@nnrp.usenet.blueworldhosting.com> Injection-Info: chiark.greenend.org.uk; posting-host="chiark.greenend.org.uk:93.93.131.173"; logging-data="23534"; mail-complaints-to="abuse@chiark.greenend.org.uk" User-Agent: tin/1.8.3-20070201 ("Scotasay") (UNIX) (Linux/5.10.0-35-amd64 (x86_64)) Originator: theom@chiark.greenend.org.uk ([93.93.131.173]) Edward Rawde wrote: > "Don Y" wrote in message news:1020c8h$2oq18$1@dont-email.me... > >I need a device that can sit midspan (at a "splice point") and monitor > > an ethernet connection for integrity. At the very least, that continuity > > exists to both ends of the span. > > > > While these are PoE/PoE+ drops, I don't want to place any significant > > burden on the PSEs; an external power supply is therefor likely. > > In that case I'd just put an unmanaged four port non PoE switch at mid run > and look into getting access to the LEDs on the switch which tell me what > the link is doing. > The last design I did which had an ethernet port used KS8721BL Won't that prevent PoE passing through the link? This switch will terminate the PoE and won't pass power or PoE signalling through to the far end. I suppose you could have some kind of relay box that normally passes the line through but interposes an ethernet switch (or something else) in the middle for testing purposes. When you're in test mode the PoE drops, but maybe you don't mind that. Or maybe you do a PoE receiver and PoE injector to let PoE pass the tester switch. Some switches can do pair tests: https://www.engineerkhan.com/networking/testing-an-ethernet-cable-from-a-cisco-switch/ Don't know what a relay would do to signal integrity though. (it probably has to be mechanical due to isolation requirements) Theo